Immunoassay of plasmonic gold‐nanoparticle clusters: Plasmon coupling effects for Parkinson biomarker detection

A simple signal‐on plasmonic optical assay for the detection of the Parkinson biomarker using gold‐nanoparticle clusters (AuNCs) for signal amplification is presented. This approach is based on the improvement of the optical density (OD) change of the plasmonic band of a localized surface plasmon resonance (LSPR) Au nanoparticle (AuNP) sensor interface using Au NCs conjugated antibodies. The amplification results in a 260‐fold improvement in concentration detection, from 1,000 ng/mL (unlabeled antibody) to 3.8 ng/mL (antibody‐conjugated AuNCs). The sensitivity enhancement can be ascribed to the further plasmonic coupling between the antibody‐conjugated AuNCs and the AuNPs on the LSPR interface and the enhanced amount of target molecule bound to the bioassay. This AuNCs‐assisted signal amplification strategy allows for improving the sensitivity of the plasmon‐based bioassays and can be extended to other optical‐based diagnostic technologies. Importantly, the simple detecting procedure and protocol assembly make it competitive with other existing sensing technologies such as ELISA, allowing for practical usage in clinical diagnostics.     

Understanding plasmonic catalysis with controlled nanomaterials based on catalytic and plasmonic metals

Recently, it has been established that the localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles can be put toward the acceleration and control of molecular transformations. This field, named plasmonic catalysis, has emerged as a new frontier in nanocatalysis. For metals such as silver (Ag), gold (Au), and copper (Cu), the LSPR excitation can take place in the visible and near-infrared ranges, opening possibilities for the conversion of solar to chemical energy and new/alternative reaction pathways not accessible via conventional, thermally activated catalytic processes. As both catalytic and optical properties can be tuned by controlling several physical and chemical parameters at the nanoscale, design-controlled nanomaterials open the door to unlock the potential of plasmonic catalysis both in terms of fundamental understanding and optimization of performances. In this context, after introducing the fundamentals of plasmonic catalysis, we provide an overview on the current understanding of this field enabled by the utilization of designed-controlled nanostructures based on plasmonic and catalytic metals as model systems. We start by discussing trends in plasmonic catalytic performances and their correlation with nanoparticle size, shape, composition, and structure. Then, we highlight how multimetallic compositions and morphologies containing both catalytic and plasmonic components enables one to extend the use of plasmonic catalysis to metals that are important in catalysis but do not support LSPR excitation in the visible range. Finally, we focus on key challenges and perspectives that are critically important to assist us in designing future energy-efficient plasmonic-catalytic materials.     

Polymer‐Supported Bimetallic Ag@AgAu Nanocomposites: Synthesis and Catalytic Properties

Supported noble bimetallic nanomaterials have attracted great interest owing to their applications in catalysis. Herein, polystyrene‐supported Ag@AgAu bimetallic nanocomposites were synthesized by using a seed‐growth route. The size and degree of coverage of the Ag@AgAu NPs could be controlled by changing the experimental parameters. SEM, TEM, STEM, EDS, and XPS analysis was used to characterize the morphology, structure, and composition of these nanocomposites. We found that the bimetallic nanoparticles on the polystyrene beads had a core–shell structure that was comprised of a Ag core and a AgAu alloy shell. The optical properties of the nanocomposites were also studied by UV/Vis/NIR spectroscopy, which indicated that the localized surface plasmon resonance (LSPR) absorptions of the nanocomposites could be tailored over a large scale from 450 nm to 950 nm. The catalytic properties of the nanocomposites were studied by using the reduction of 4‐nitrophenol (4‐NP) by NaBH₄ as a model system. The results showed that the catalytic activity of the polystyrene‐supported Ag@AgAu bimetallic nanocomposites was remarkably superior to that of polystyrene‐supported monometallic Ag and Au nanocomposites with the same nanoparticle size. In addition, an investigation of the recycling catalytic activity of the PS‐Ag@AgAu nanocomposites revealed that the catalyst possessed good stability. The enhancement of the catalytic activity was proposed to be due to the ligand and strain effects between Ag and Au.     

Au纳米粒子表面附近偶氮苯分子的吸收光谱

我们将时空间含时密度泛函理论与经典的电动力学时空间有限差分技术相结合,对吸附在Au纳米粒子表面附近的偶氮苯分子顺式和反式两种同分异构体的光学性质进行了研究。计算结果显示,一方面表面等离子激元共振会增大其周围激光外场的强度,从而使得偶氮苯分子的吸收光谱得到增强,另一方面,吸附分子与金属纳米粒子之间的相互耦合作用也会对一些低能特殊谱峰的强度及位置产生影响,从而使得谱线的形状与单独的偶氮苯分子或Au纳米粒子并不相同。此外,等离子激元的增强效应会随着分子与金属纳米粒子之间的距离以及纳米粒子尺寸的变化而发生变化。     

Binary Au/MWCNT and Ternary Au/ZnO/MWCNT Nanocomposites: Synthesis,Characterisation and Catalytic Performance

Gold nanoparticles of 10–24 and 5–8 nm in size were obtained by chemical citrate reduction and UV photoreduction, respectively, on acid‐treated multiwalled carbon nanotubes (MWCNTs) and on ZnO/MWCNT composites. The shape and size of the deposited Au nanoparticles were found to be dependent upon the synthetic method used. Single‐crystalline, hexagonal gold particles were produced in the case of UV photoreduction on ZnO/MWCNT, whereas spherical Au particles were deposited on MWCNT when the chemical citrate reduction method was used. In the UV photoreduction route, n‐doped ZnO serves as the e^? donor, whereas the solvent is the hole trap. All materials were fully characterised by UV/Vis spectroscopy, scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, Raman spectroscopy and BET surface analysis. The catalytic activity of the composites was studied for the selective hydrogenation of α,β‐unsaturated carbonyl compound 3,7‐dimethyl‐2,6‐octadienal (citral). The Au/ZnO/MWCNT composite favours the formation of unsaturated alcohols (selectivity=50 % at a citral conversion of 20 %) due to the presence of single‐crystalline, hexagonal gold particles, whereas saturated aldehyde formation is favoured in the case of the Au/MWCNT nanocomposite that contains spherical gold particles.     

Fourier Transform Surface Plasmon Resonance (FTSPR) with Gyromagnetic Plasmonic Nanorods

An unprecedented active and dynamic sensing platform based on a LSPR configuration that is modulated by using an external magnetic field is reported. Electrochemically synthesized Au/Fe/Au nanorods exhibited plasmonically active behavior through plasmonic coupling, and the middle ferromagnetic Fe block responded to a magnetic impetus, allowing the nanorods to be modulated. The shear force variation induced by the specific binding events between antigens and antibodies on the nanorod surface is used to enhance the sensitivity of detection of antigens in the plasmonics‐based sensor application. As a proof‐of‐concept, influenza A virus (HA1) was used as a target protein. The limit of detection was enhanced by two orders of magnitude compared to that of traditional LSPR sensing.     

Dodecahedral Au/Pt Nanobowls as Robust Plasmonic Electrocatalysts for Methanol Oxidation under Visible-Light Illumination

Plasmonic nanostructures with large absorption areas under resonant excitation have been utilized extensively in photon-assisted applications. In this work, dodecahedral Au nanobowls were first prepared by an easy and template-free method only through the introduction of H₂PtCl₆ and I⁻ during the growth procedure. The Au nanobowls show electron-field enhancement due to the high curvature of the bowl edge, the open region, and dodecahedral morphology. Au/Pt nanobowls, which couple plasmonic Au and catalytic Pt, were then constructed as plasmonic electrocatalysts for methanol oxidation. The mass activity reached 497.6 mA mg⁻¹ under visible-light illumination, which is 1.9 times that measured in the dark. Simultaneously, the electrocatalytic stability is also greatly improved under light excitation. The enhanced properties of the plasmonic Au/Pt electrocatalysts are ascribed to the synergistic effect of the plasmon-enhanced photothermal and hot-carrier effects on the basis of experimental investigations. This work thus offers an effective methodology to construct efficient plasmonic electrocatalysts for fuel cells.     

Room‐Temperature and Aqueous‐Phase Synthesis of Plasmonic Molybdenum Oxide Nanoparticles for Visible‐Light‐Enhanced Hydrogen Generation

A straightforward aqueous synthesis of MoO_3?x nanoparticles at room temperature was developed by using (NH₄)₆Mo₇O₂₄?4 H₂O and MoCl₅ as precursors in the absence of reductants, inert gas, and organic solvents. SEM and TEM images indicate the as‐prepared products are nanoparticles with diameters of 90–180 nm. The diffuse reflectance UV‐visible‐near‐IR spectra of the samples indicate localized surface plasmon resonance (LSPR) properties generated by the introduction of oxygen vacancies. Owing to its strong plasmonic absorption in the visible‐light and near‐infrared region, such nanostructures exhibit an enhancement of activity toward visible‐light catalytic hydrogen generation. MoO_3?x nanoparticles synthesized with a molar ratio of Mo^VI/Mo^V 1:1 show the highest yield of H₂ evolution. The cycling catalytic performance has been investigated to indicate the structural and chemical stability of the as‐prepared plasmonic MoO_3?x nanoparticles, which reveals its potential application in visible‐light catalytic hydrogen production.     

Plasmonic/Nonlinear Optical Material Core/Shell Nanorods as Nanoscale Plasmon Modulators and Optical Voltage Sensors

Herein, we report the design and synthesis of plasmonic/non‐linear optical (NLO) material core/shell nanostructures that can allow dynamic manipulation of light signals using an external electrical field and enable a new generation of nanoscale optical voltage sensors. We show that gold nanorods (Au NRs) can be synthesized with tunable plasmonic properties and function as the nucleation seeds for continued growth of a shell of NLO materials (such as polyaniline, PANI) with variable thickness. The formation of a PANI nanoshell allows dynamic modulation of the dielectric environment of the plasmonic Au NRs, and therefore the plasmonic resonance characteristics, by an external electrical field. The finite element simulation confirms that such modulation is originated from the field‐induced modulation of the dielectric constant of the NLO shell. This approach is general, and the coating of the Au NRs with other NLO materials (such as barium titanate, BTO) is found to produce a similar effect. These findings can not only open a new pathway to active modulation of plasmonic resonance at the sub‐wavelength scale but also enable the creation of a new generation of nanoscale optical voltage sensors (NOVS).     

Fine‐Tuning the Homometallic Interface of Au‐on‐Au Nanorods and Their Photothermal Therapy in the NIR‐II Window

The localized surface plasmon resonance (LSPR) of plasmonic nanomaterials is highly dependent on their structures. Going beyond simple shape and size, further structural diversification demands the growth of non‐wetting domains. Now, two new dimensions of synthetic controls in Au‐on‐Au homometallic nanohybrids are presented: the number of the Au islands and the emerging shapes. By controlling the interfacial energy and growth kinetics, a series of Au‐on‐AuNR hybrid structures are successfully obtained, with the newly grown Au domains being sphere and branched wire (nanocoral). The structural variety allowed the LSPR to be fine‐tuned in full spectrum range, making them excellent candidates for plasmonic applications. The nanocorals exhibit black‐body absorption and outstanding photothermal conversion capability in NIR‐II window. In vitro and in vivo experiments verified them as excellent photothermal therapy and photoacoustic imaging agents.     

Ag纳米粒子修饰光纤探针在等离激元催化反应中的应用

本文发展了一种基于Ag纳米粒子(AgNPs)修饰的局域表面等离激元共振(LSPR)光纤探针,作为等离激元催化反应基底同时原位检测表面增强拉曼光谱(SERS)信号,实现反应与检测一体化。本文使用(3-氨基丙基)三甲氧基硅烷(APTMS)分子将AgNPs组装到光纤探针表面。通过调控自组装时间,可形成AgNPs均匀分布的探针。以对巯基苯胺(PATP)作为反应的模型分子,获得了较好的等离激元催化及信号检测效果。在相同光源条件下,从光纤内部激发收集所得产物的SERS信号强度为外部激发收集的12.8倍,表明内激发收集方式在反应及信号检测方面具有优势;在一定浓度范围(10~(-4)–10~(-8)mol·L~(-1))内可用该光纤探针对PATP溶液进行定量分析;运用该光纤探针开展了等离激元催化PATP分子偶联反应的原位动力学研究。该LSPR光纤探针具有较高灵敏度,对样品损伤小,可在多场合下实现原位检测,且制备简便、成本较低。还有望结合近场扫描光学显微技术进一步对样品表面进行微区等离激元催化反应及检测并得到反应的二维分布图。     

Synergy between Plasmonic and Electrocatalytic Activation of Methanol Oxidation on Palladium–Silver Alloy Nanotubes

Localized surface plasmon resonance (LSPR) excitation of noble metal nanoparticles has been shown to accelerate and drive photochemical reactions. Here, LSPR excitation is shown to enhance the electrocatalysis of a fuel‐cell‐relevant reaction. The electrocatalyst consists of Pd_xAg alloy nanotubes (NTs), which combine the catalytic activity of Pd toward the methanol oxidation reaction (MOR) and the visible‐light plasmonic response of Ag. The alloy electrocatalyst exhibits enhanced MOR activity under LSPR excitation with significantly higher current densities and a shift to more positive potentials. The modulation of MOR activity is ascribed primarily to hot holes generated by LSPR excitation of the Pd_xAg NTs.     

Template-free Polyoxometalate-assisted Synthesis of Au/ZnO Hollow Sphere Hererostructures for Photocatalytic Water Purification

The controlled synthesis of ZnO hollow spheres is successfully achieved through a facile solvothermal method using a Keggin-type silicotungstic acid(H_4 Si(W_3 O_(10))_4:HSW) as structure directing agent. The formation process of these hollow spheres is proposed based on a variety of controlled experiments. In addition, Au nanoparticles are loaded onto the surface of ZnO hollow spheres. It is found that the Au-loaded ZnO(Au/ZnO) composites exhibit greatly enhanced activity on oxidizing Rhodamine B(Rh B) under simulated UV or visible light irradiation, compared to the pristine ZnO hollow spheres. The improved performance of Au/ZnO heterostructures is mainly attributed to the enhanced optical absorption and the accelerated separation and migration of photogenerated charge carriers. Moreover, the photocatalytic reaction mechanisms are proposed based on the results of electron spin resonance(ESR) analysis, photoelectrochemical measurements, and photocatalytic evaluation. The results and findings are expected to provide significance to the synthesis of noble metal-semiconductor hybrids towards water purification.     

Plasmonic enhancements of photocatalytic activity of Pt/n-Si/Ag photodiodes using Au/Ag core/shell nanorods

We report the plasmonic enhancement of the photocatalytic properties of Pt/n-Si/Ag photodiode photocatalysts using Au/Ag core/shell nanorods. We show that Au/Ag core/shell nanorods can be synthesized with tunable plasmon resonance frequencies and then conjugated onto Pt/n-Si/Ag photodiodes using well-defined chemistry. Photocatalytic studies showed that the conjugation with Au/Ag core/shell nanorods can significantly enhance the photocatalytic activity by more than a factor of 3. Spectral dependence studies further revealed that the photocatalytic enhancement is strongly correlated with the plasmonic absorption spectra of the Au/Ag core/shell nanorods, unambiguously demonstrating the plasmonic enhancement effect.     

Resolving Optical and Catalytic Activities in Thermoresponsive Nanoparticles by Permanent Ligation with Temperature‐Sensitive Polymers

Thermoresponsive nanoparticles (NPs) represent an important hybrid material comprising functional NPs with temperature‐sensitive polymer ligands. Strikingly, significant discrepancies in optical and catalytic properties of thermoresponsive noble‐metal NPs have been reported, and have yet to be unraveled. Reported herein is the crafting of Au NPs, intimately and permanently ligated by thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM), in situ using a starlike block copolymer nanoreactor as model system to resolve the paradox noted above. As temperature rises, plasmonic absorption of PNIPAM‐capped Au NPs red‐shifts with increased intensity in the absence of free linear PNIPAM, whereas a greater red‐shift with decreased intensity occurs in the presence of deliberately introduced linear PNIPAM. Remarkably, the absence or addition of free linear PNIPAM also accounts for non‐monotonic or switchable on/off catalytic performance, respectively, of PNIPAM‐capped Au NPs.     

Development of silver/gold nanocages onto indium tin oxide glass as a reagentless plasmonic mercury sensor

We demonstrate the utilization of silver/gold nanocages (Ag/Au NCs) deposited onto transparent indium tin oxide (ITO) film glass as the basis of a reagentless, simple and inexpensive mercury probe. The localized surface plasmon resonance (LSPR) peak wavelength was located at ∼800 nm. By utilizing the redox reaction between Hg²⁺ ions and Ag atoms that existed in Ag/Au NCs, the LSPR peak of Ag/Au NCs was blue-shifted. Thus, we develop an optical sensing probe for the detection of Hg²⁺ ions. The LSPR peak changes were lineally proportional to the concentration of Hg²⁺ ions over the range from 10 ppb to 0.5 ppm. The detection limit was ∼5 ppb. This plasmonic probe shows good selectivity and high sensitivity. The proposed optical probe is successfully applied to the sensing of Hg²⁺ in real samples.     

AuNPs/PNIPAM复合颗粒的制备及其温敏性质

将金纳米颗粒(AuNPs)组装到聚N-异丙基丙烯酰胺(PNIPAM)水凝胶微球表面制备出AuNPs/PNIPAM复合颗粒. 将PNIPAM 凝胶的温敏特性与AuNPs的光学性质结合, 通过改变温度调节AuNPs的局部表面等离子共振(LSPR)吸收峰位置. 研究结果表明, 温度升高使AuNPs的LSPR吸收峰发生红移, 并且这种效应是可逆的. 同时发现, AuNPs的光学性质还可以作为表征PNIPAM水凝胶微球温敏行为的一种手段. 利用透射电镜、紫外-可见光谱仪及动态光散射仪对AuNPs/PNIPAM复合颗粒的形貌、光学性质、粒径变化等进行了分析.     

Surface Plasmon Resonance‐Enhanced Visible‐NIR‐Driven Photocatalytic and Photothermal Catalytic Performance by Ag/Mesoporous Black TiO2 Nanotube Heterojunctions

Ag/mesoporous black TiO₂ nanotubes heterojunctions (Ag‐MBTHs) were fabricated through a surface hydrogenation, wet‐impregnation and photoreduction strategy. The as‐prepared Ag‐MBTHs possess a relatively high specific surface area of ≈85 m² g^?1 and an average pore size of ≈13.2 nm. The Ag‐MBTHs with a narrow band gap of ≈2.63 eV extend the photoresponse from UV to the visible‐light and near‐infrared (NIR) region. They exhibit excellent visible‐NIR‐driven photothermal catalytic and photocatalytic performance for complete conversion of nitro aromatic compounds (100 %) and mineralization of highly toxic phenol (100 %). The enhancement can be attributed to the mesoporous hollow structures increasing the light multi‐refraction, the Ti³⁺ in frameworks and the surface plasmon resonance (SPR) effect of plasmonic Ag nanoparticles favoring light‐harvesting and spatial separation of photogenerated electron–hole pairs, which is confirmed by transient fluorescence. The fabrication of this SPR‐enhanced visible‐NIR‐driven Ag‐MBTHs catalyst may provide new insights for designing other high‐performance heterojunctions as photocatalytic and photothermal catalytic nanomaterials.     

Controlled dispersion of polystyrene‐capped Au nanoparticles in P3HT:PC61BM and consequences upon active layer nanostructure

Numerous recent publications detail higher absorption and photovoltaic performance within organic photovoltaic (OPV) devices which are loaded with Au or Ag nanoparticles to leverage the light management properties of the localized surface plasmon resonance (LSPR). This report details the impact upon film morphology and polymer/nanoparticle interactions caused by incorporation of polystyrene‐coated Au nanoparticles (Au/PS) into the P3HT:PC₆₁BM bulk heterojunction film. Nanostructural analysis by transmission electron microscopy and X‐ray scattering reveals tunable Au/PS particle assembly that depends upon the choice of casting solvent, polymer chain length, film drying time, and Au/PS particle loading density. This Au/PS particle assembly has implications on the spectral position of the Au nanoparticle LSPR, which shifts from 535 nm for individually dispersed particles in toluene to 650 nm for particles arranged in large clusters within the P3HT:PC₆₁BM matrix. These results suggest a critical impact from PS/P3HT phase separation, which causes controlled assembly of a separate Au/PS phase in the nanoparticle/OPV composite; controlled Au/PS phase formation provides a blueprint for designing AuNP/OPV hybrid films that impart tunable optical behavior and potentially improve photovoltaic performance. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 709–720     

Nanostructured materials with localized surface plasmon resonance for photocatalysis

Localized surface plasmon resonance（LSPR） enhanced photocatalysis has fascinated much interest and considerable efforts have been devoted toward the development of plasmonic photocatalysts.In the past decades,noble metal nanoparticles（Au and Ag） with LSPR feature have found wide applications in solar energy conversion.Numerous metal-based photocatalysts have been proposed including metal/semiconductor heterostructures and plasmonic bimetallic or multimetallic nanostructures.However,high cost and...